Better Battery Runtimes Without Characterization

Better Battery Runtimes Without Characterization

If the battery-life indicator on your smartphone tells you that you’ve got 30% charge left, then you might feel reassured enough to proceed with an important conference call with a big client without reaching for your charger. But what if your battery was actually at only a 5% charge and the phone died during the middle of an important conversation?

Accurate battery runtime calls for highly accurate fuel gauges. The impact that temperature and load have on voltage, however, has made fuel gauging challenging. Traditionally, battery fuel gauges have been quite dependent on the battery type involved. As a result, the gauges have had to be tailored to each battery, a process that requires time-consuming characterization in a lab under various load and temperature conditions.

Simple, or immediate, voltage presents one way to perform fuel gauging. But examining voltage only isn’t always a good estimator of battery state-of-charge because of how cell materials and temperature impact voltage in a time-dependent manner. Using simple voltage, the most accurate readings come after the battery rests in an open-circuit state for at least a couple of hours. So, this approach isn’t very practical.

Coulomb counting offers another fuel-gauging method, measuring the current that’s constantly going in and out of the battery. To indicate how much charge remains overall, the estimated charge used by a given device is subtracted from the total charge that can be held by the battery. Coulomb counting is fine for short-term accuracy, but the method’s big disadvantage is that it suffers from offset accumulation drift. A seemingly small error can result in a big discrepancy in accuracy and, eventually, lead to the device shutting down prematurely or abruptly crashing.

Highly Accurate Fuel Gauge with Low Quiescent Current

Now, you no longer have to make fuel-gauging trade-offs. Maxim has unveiled a new high-accuracy, low quiescent current fuel gauge that helps maximize battery runtimes without requiring time-consuming, labor-intensive battery characterization. The MAX17055 ModelGauge m5 is ideal for portable device designers who are looking for an easier way to design in accurate, low-power host-side battery gauges. The MAX17055 provides the industry’s most accurate fuel gauge—within 1% state-of-charge (SOC) error in most cases. That means that you can plan for a device shutdown that maximizes the device runtime. The gauge also draws the industry’s lowest quiescent current—7µA in the low-power operating mode—and is available in a 1.4mm x 1.5mm WLP for applications requiring small form factors.

Over the years, Maxim has shipped more than 1.3 billion fuel gauges, characterized more than 2,000 batteries, and analyzed more than 80 battery years worth of data. Our ModelGaugeTm technology converts real-time electrical measurements into usable SOC percentages and other battery information. ModelGauge m5 is the latest version of the algorithm and its EZ configuration, available in the MAX17055, eliminates battery characterization for many applications. Maxim maintains a vast battery database containing cell characteristics and behavior over various test conditions. The database allows Maxim to validate any new enhancements in the ModelGauge algorithm.

Figure 1. MAX17055 sub-system block diagram.

The MAX17055 is ideal for designs using a one-cell lithium ion/polymer battery. Learn more about fuel gauging in this document, "Accurate Technology for Easy, Secure Fuel Gauging You Can Trust" (PDF).